We are studying command elements and related interneurons in the abdominal ganglia of crustaceans and how they control abdominal positioning and limb movement in the posterior metameres. The system incorporates many hundreds of neurons and in sufficiently complex to serve as a model for a vertebrate episodic behavior. We are applying the techniques of intracellular electrophysiology, dye-filling, cellular morphology, immunocytochemistry and the mathematics of population biology to the problem. The following projects are proposed. Since our command elements are known to work in groups, we have devised a means of estimating the size and coherence of these groups. The abdominal skeleton, muscles and gross nervous system are serially homologous in the decapod crustacean abdomen, yet our preliminary evidence indicates the controlling command elements are not. We are studying how this arrangement can work and how it evolved. This study should be fundamental interest because the vertebrates are also metameric. Next, our population studies be of fundamental interest, because the vertebrates are also metameric. Next, our population studies showed that certain types of command elements are encountered more frequently than is dictated by chance. A project is outline to examine the possibility that they are "duplicated." Multiple copies of cells in this preparation are heretofore unknown, but if so, identification of such cells would be particularly difficult thus limiting their use severely. Next, we propose to assign transmitters to some of the identified command elements that function in this system. Knowing the transmitters would allow many pharmacological studies not now possible. We are completing two other studies, how command elements fire during normal behavior, and finally we are studying processes common to the behavioral repertory of all animals, i.e., the role of command elements in coordinating and sequencing two behaviors.